powering LED strip through USB... is it safe?

Mahbub · February 25, 2021

so i have this cheap 12volt led strip laying around, and i saw a youtube tutorial where a guy soldered a usb wire to the led strip and when he plugged it into his pc.. it lit up.. my question is will the led lit up less brightly because the usb will provide 5 volts and not 12 volts, or will the led try and forcefully try and take 12 volt and harm the usb port in the long run?

mariushm · February 25, 2021

It was probably a 5v led strip, or the guy was lying for views.

A 12v led strip will have several leds in series, for example 3 leds.

A led has a minimum forward voltage, the point from where it actually produces light... let's say for a white or blue led that minimum voltage is around 2.8v..3.2v , for red it's around 1.6v..2v and for other colors (depending on chemistry) around 2v..2.4v

To make a led strip run at 12v, they typically make a series (chain) of 3 leds and a resistor which limits the current dropping the remaining voltage :

[+12v] ----- [ led 1 = 2.8..3.2v ]---- [ led 2 = 2.8..3.2v ] ---- [ led 3 = 2.8..3.2v ] ----- [=== resistor 12v - 3x (2.8..3.2v) = 3.6 .. 2.4 v ==== ] ----- [ GROUND]

With 5v, it's simply not possible to have a high enough voltage to go above the minimum forward voltage ... only way it could work if you would short (connect both + and - together) 2 out of the 3 leds so the current jumps over them and now you have a single led in each group of leds.

Another option would be to buy a step-up dc-dc converter which can take 5v from USB and boosts the voltage up to at least 10v or whatever the minimum is required for the led strip to work. Such DC-DC converters can be super cheap, as low as 1-2$ on ebay.

LogicalDrm · February 25, 2021

-> Moved to Cases and Mods

thrasher_565 · February 26, 2021

16 hours ago, Mahbub said:

so i have this cheap 12volt led strip laying around, and i saw a youtube tutorial where a guy soldered a usb wire to the led strip and when he plugged it into his pc.. it lit up.. my question is will the led lit up less brightly because the usb will provide 5 volts and not 12 volts, or will the led try and forcefully try and take 12 volt and harm the usb port in the long run?

you can buy 5v rgb strips as well as 12v argb strips.